Sporting are also due to take on Germany's Schalke and Slovenian's Maribor - who knocked out Scottish champions Celtic in the qualifiers - in Group G.

Gauld, 18, signed a six-year contact with a 60m euro (£48m) buyout clause with Sporting Lisbon.

The Scotland Under-21 player scored eight goals in 38 games last term in the Scottish Premiership.

He impressed last season during a campaign that saw United finish fourth in the Premiership and runners-up in the Scottish Cup, and was shortlisted for the PFA Scotland Young Player of the Year award, which was won by team-mate Andrew Robertson.

Having made his United debut in May 2012, his rise to prominence led to an extended contract at Tannadice as soon as he turned 18.